This disclosure is generally directed to photoreceptors, photoconductors, xerographic imaging members, and the like. More specifically, the present disclosure is directed to multilayered drum, or flexible belt imaging members, or devices comprised of a first layer, a supporting medium like a substrate, a photogenerating layer, and a charge transport layer, including a plurality of charge transport layers, such as a first charge transport layer and a second charge transport layer, an optional adhesive layer, an optional hole blocking or undercoat layer, and an optional overcoat layer, and wherein the supporting substrate is situated between the first layer and the photogenerating layer. More specifically, the photoconductors disclosed, which in embodiments permit acceptable anticurl characteristics in combination with excellent conductivity, prolonged wear, surface slipperiness, and scratch resistant characteristics, contain a first backside coating layer or curl deterring backside coating layer (ACBC), and which layer is in contact with and contiguous to the reverse side of the supporting substrate, that is this side of the substrate that is not in contact with the photogenerating layer, and which first layer, or ACBC layer of the present disclosure, is comprised of a polyurethane, and optionally where the polyurethane can be deposited on a polymer layer, such as a polycarbonate.
The backside coating layer illustrated herein can be efficiently prepared, and in embodiments, the ACBC coating layer has excellent wear resistance, extended lifetimes, minimal dust and charge buildup, excellent bulk conductivity, possesses antistatic properties, acceptable surface resistivities, such as a surface resistivity of from about 107 to about 1010 ohm/sq., and permit the elimination or minimization of photoconductive imaging member belt ACBC scratches.
The ACBC layer of the present disclosure, in embodiments, possesses a slippery surface, thus the wear resistance of this layer is excellent, especially as compared to an ACBC layer without any polyurethane, or an ACBC layer containing a polytetrafluoroethylene (PTFE). Also, a coating dispersion containing the polyurethane component is stable for extended time periods; minimal agglomeration of the ACBC layer components is provided, thereby increasing the coating uniformity of this layer; and other advantages as illustrated herein for photoconductors with ACBC layers comprising a polyurethane component.
More specifically, there is disclosed a photoconductor that includes an ACBC layer comprised of self conducting polyurethane with, for example, a surface resistivity of from about 107 to about 1010 ohm/sq, and where the addition to the ACBC layer of conventional conductive components, such as carbon black, carbon nanotube, or metal oxide, are avoided, which polyurethane is comprised of a dendritic or branched polyester polyol and a polyisocyanate, and more specifically, a blocked polyisocyanate, or in embodiments a polyurethane ACBC layer formed by the reaction of a dendritic polyester polyol and a blocked polyisocyanate.
The disclosed polyurethane ACBC layer further comprises a siloxane component or a fluoro component, which co-crosslinks with the resin blend and provides the ACBC with slippery characteristics, and where slipperiness of the disclosed homogeneous ACBC layer can be adjusted by varying the amount of the siloxane or fluoro component selected.
In some instances, when a flexible layered photoconductor belt is mounted over a belt support module comprising various supporting rollers and backer bars present in a xerographic imaging apparatus, the anticurl or reduction in curl backside coating (ACBC), functioning under a normal xerographic machine operation condition, is repeatedly subjected to mechanical sliding contact against the apparatus backer bars and the belt support module rollers to thereby adversely impact the ACBC wear characteristics. Moreover, with a number of known prior art ACBC photoconductor layers formulated, the mechanical interactions against the belt support module components can decrease the lifetime of the photoconductor primarily because of wear and degradation after short time periods.
In embodiments, the photoconductors disclosed include an ACBC (anticurl backside coating) layer on the reverse side of the supporting substrate of a belt photoreceptor. The ACBC layer, which can be solution coated, for example, as a self-adhesive layer on the reverse side of the substrate of the photoconductor, comprises known suitable polyurethane components, such as commercially available polyurethanes, that, for example, substantially reduce surface contact friction, minimize or avoid curl, and prevent or minimize wear/scratch problems for the photoconductor. In embodiments, the mechanically robust ACBC layer of the present disclosure usually will not substantially reduce the layers thickness over extended time periods adversely affecting its anticurl ability for maintaining effective imaging member belt flatness while minimizing the formation of dirt and debris.
High surface contact friction of the backside coating against xerographic machines, such as printers, and its subsystems can cause the development of undesirable electrostatic charge buildup. In a number of instances, with devices, such as printers, the electrostatic charge builds up because of high contact friction between the anticurl backside coating and the backer bars which increases the frictional force to the point that it requires higher torque from the driving motor to pull the belt for effective cycling motion. In a full color electrophotographic apparatus using a 10-pitch photoreceptor belt, this electrostatic charge buildup can be high due to the large number of backer bars used in the machine. These and other disadvantages are minimized or avoided with the polyurethane containing photoconductors illustrated herein in embodiments.
Yet more specifically, there is desired an ACBC containing photoconductor with intrinsic properties that minimize or eliminate charge accumulation in the photoconductor without sacrificing other electrical properties and also possessing low surface energy characteristics. One known ACBC design can be designated as an insulating polymer coating containing additives, such as silica, PTFE or TEFLON®, in an attempt to reduce friction against backer plates and rollers, but these additives tend to charge up triboelectrically due to their rubbing against the plates resulting in an electrostatic drag force that adversely affects the process speed of the photoconductor.
Belt modules that incorporate sliding positioning supports like production xerographic printing machines generate a large amount of electric charge from the sliding contact that is discharged by the use of a somewhat costly combination of a carbon fiber brush and a bias power supply. Failure to discharge the ACBC layer produces an electrostatic attractive force between the photoreceptor and the support element which increases the normal force producing more drag which complicates photoreceptor belt removal, and can become large enough to stall or render inoperative the drive motor. In addition, the multiple points of sliding contact generate a significant quantity of fine polymer dust which coats the machine components and acts as a lubricant, reducing drive roller capacity. These and other related disadvantages are minimized in embodiments, with the ACBC containing photoconductors disclosed herein.
Also included within the scope of the present disclosure are methods of imaging and printing with the photoresponsive or photoconductor devices illustrated herein. These methods generally involve the formation of an electrostatic latent image on the imaging member, followed by developing the image with a toner composition comprised, for example, of thermoplastic resin, colorant, such as pigment, charge additive, and surface additive, reference U.S. Pat. Nos. 4,560,635; 4,298,697 and 4,338,390, the disclosures of which are totally incorporated herein by reference, subsequently transferring the toner image to a suitable image receiving substrate, and permanently affixing the image thereto. In those environments wherein the device is to be used in a printing mode, the imaging method involves the same operation with the exception that exposure can be accomplished with a laser device or image bar. More specifically, the flexible photoconductor belts disclosed herein can be selected for the Xerox Corporation iGEN® machines that generate with some versions over 100 copies per minute. Processes of imaging, especially xerographic imaging and printing, including digital and/or color printing, are thus encompassed by the present disclosure. The imaging members are, in embodiments, sensitive in the wavelength region of, for example, from about 400 to about 900 nanometers, and in particular from about 650 to about 850 nanometers, thus diode lasers can be selected as the light source. Moreover, the imaging members of this disclosure are useful in color xerographic applications, particularly high-speed color copying and printing processes.